In U.S. Pat. No. 3,853,932, the applicant herein has disclosed and claimed a process for converting the fluorosilicone cyclic siloxane trimer, 2,4,6-tris(3,3,3-trifluoropropyl)-2,4,6-trimethylcyclotrisiloxane, to the corresponding linear "trimer diol", HO--CF.sub.3 CH.sub.2 CH.sub.2 (CH.sub.3)SiO.sub.x H, wherein x averages 3 to 5, using an acid-activated hydroaluminum silicate clay in the presence of water. It has now been unexpectedly discovered that this "trimer diol" can be condensed to high molecular weight polymers and copolymers in high yield without the formation of any appreciable quantities of cyclics.
Such a result is completely unexpected because Brown, U.S. Pat. No. 3,373,138, teaches that a trifluoropropyl diol of the same average composition of the "trimer diol" cannot be condensed to high molecular weight polymer without the formation of large quantities of cyclics. Moreover, the Brown patent teaches that a linear fluorosilicone of the same average composition as the "trimer diol" must be aged in contact with an aqueous solution of above pH 7 for several hours to three months to form at least the hexamer diol. Hexamer diol and higher diols can then be condensed to high molecular weight with the formation of only small amounts of cyclic by-products.
According to the present invention, a trimer diol as described in the U.S. Pat. No. 3,853,932 can be converted to high molecular weight polymer by adding a non-rearranging condensation catalyst such as tin salts of carboxylic acids, amines, and amine salts and removing the formed water of condensation. Polymers of penetration of more than 100 (0.1 mm/min) can be produced by this process proving that the molecular weight is high enough for the preparation of silicone rubber.
Moreover, by combining a fluorosilicone "trimer diol" with a corresponding diorgano, e.g., dimethyl silicone diol, which is miscible with the fluorosilicone oil, and then adding such a condensation catalyst, fluorosilicone-methyl copolymers and block copolymers can be easily produced. For example, copolymers can be produced at not only 25, 50, 75, and 90 mol % trifluoropropylorganosiloxy content, but also at any other composition.
The process of this invention provides ready access to fluorosilicone copolymers of more than 20 mol % fluoro silicone content at high molecular weights. Previously, if the full solvent resistance offered by a 100 mol % trifluoropropyl polymer was not needed, then the fluorosilicone was blended with a diorganopolysiloxane gum. However, a copolymer of trifluoropropyl and an organosilicone has been found to have better solvent resistance than a fluorosilicone/organosilicone blend at the same fluorosilicone content and thus the present process provides a superior product.
It is, accordingly, a principal object of the present invention to provide a process for producing fluoroalkyl-substituted diorganopolysiloxane homo- or copolymer gums in high yield, using a low molecular weight silanol end-stopped polysiloxane, and especially those produced from cyclic trisiloxanes by reaction with water in the presence of an acid-treated clay.
Another object of the present invention is to provide fluorine-containing diorganopolysiloxane homo-and copolymer gums having a viscosity from 2,000 to 200,000,000 centipoise at 25.degree. C. by a process comprising polymerizing a silanol end-stopped fluorine-substituted low molecular weight siloxane trimer, alone, or in admixture with a silanol endstopped co-monomer in the presence of a non-bond-rearranging catalyst.
A further object of the present invention is to provide fluorine-containing diorganopolysiloxane copolymer gums having a viscosity from 2,000 to 200,000,000 centipoise at 25.degree. C., wherein at least one of the co-monomers comprises 20 to 98 mol % of the copolymer units, and includes organo groups attached to the silicon atoms having at least 3 carbon atoms, and, particularly, a --CH.sub.2 CH.sub.2 R.sup.7 substituent group, where R.sup.7 is a perfluoroalkyl group.